Polyolefin production

ABSTRACT

Use of a metallocene compound of general formula Ind 2 R″MQ 2  as a component of a catalyst system for the production of a polyethylene copolymer substantially in the absence of comonomer, wherein each Ind is the same or different and is indenyl or substituted indenyl; R″ is a bridge which comprises a C 1  to C 4  alkylene radical, a dialkyl germanium or silicon or siloxane, alkyl phosphine or amine, which bridge is substituted or unsubstituted, M is a Group IV metal or vanadium and each Q is hydrocarbyl having 1 to 20 carbon atoms or halogen; and the ratio of meso to racemic forms of the metallocene in the catalyst system is at least 1:3.

FIELD OF INVENTION

[0001] The present invention relates to a process for the preparation ofpolyethylenes and to the use of metallocene compounds as catalystcomponents for use in such a process.

BACKGROUND TO THE INVENTION

[0002] Metallocene-catalysed polymerisation of ethylene is well-knownand it is common practice to add to the ethylene monomer a comonomersuch as butene. This has the advantage of modifying the properties ofthe polyethylene so as to make a range of copolymer products withvarious mechanical properties.

[0003] Racemic (bis indenyl) ethane zirconium dichloride complexes areknown to he very active polymerisation catalysts for the production ofpolyethylene and low molecular weight isotactic polypropylene incombination with a cocatalyst such as methyl aluminoxane. Theconventional synthetic procedures for producing the racemic complexesalso produce a side product, which is the meso isomer, at a typicallevel of 3-5%.

[0004] CA-A-2104036 is directed to the use of various rac/meso mixturesprimarily as catalysts in the production of isotactic polypropylenes.This patent application also discloses the use of the meso form ofcertain metallocenes to produce atactic polypropylene. In one example,this patent application also discloses the use of a 95:5 rac/mesometallocene in the production of a propylene, ethylene block copolymer.

[0005] EP-A-0743324 is directed to a process for producing polyethyleneunder gas phase polymerisation conditions. Ethylene is polymerised inthe presence of hexene comonomer using a mixture of racemic and mesastereoisomers of a bridged metallocene catalyst.

[0006] EP-A-0643078 describe preparation of ethylene homopolymers usinga meso-ethylene-bis-(4,7-dimethyl-1-indenyl) zirconium dichloridecatalyst. The same catalyst is also used to produce an ethylene/1-butenecopolymer by copolymerising ethylene and 1-butene.

[0007] C-A-2017190 and its corresponding EP-A-0399348 disclose the useof a broad range of metallocene catalysts in the preparation ofethylene, homopolymers or in the preparation of ethylene copolymers bycopolymerisation of ethylene with 1-olefins having 3 to 20 carbon atoms.

[0008] EP-A-0835886 is directed to a process for preparing ameso/racemic metallocene compound and a process for the polymerisationor copolymerisation of olefins.

SUMMARY OF THE INVENTION

[0009] The present applicants have surprisingly found that the meso formof certain metallocenes can be advantageously used as a catalyst in theproduction of ethylene copolymers without the need to add exogenousbutene to the reaction mix.

[0010] The present invention provides use of a metallocene compound ofgeneral formula Ind₂R″MQ₂ as a component of a catalyst system for theproduction of a polyethylene copolymer substantially in the absence ofcomonomer, wherein each Ind is the same or different and is indenyl orsubstituted indenyl; R″ is a bridge which comprises a C₁ to C₄ alkyleneradical, a dialkyl germanium or silicon or siloxane, alkyl phosphine oramine, which bridge is substituted or unsubstituted M is a Group IVmetal or vanadium and each Q is hydrocarbyl having 1 to 20 carbon atomsor halogen; and the ratio of meso to racemic forms of the metallocene inthe catalyst system is at least 1:3.

[0011] The present invention further provides a process for thepreparation of a polyethylene copolymer, which comprises polymerisingethylene, optionally with hydrogen, in a substantially comonomer-freereaction medium which comprises a catalyst system comprising

[0012] (a) a metallocene compound of general formula Ind₂R″MQ₂ asdefined in any one of claims 1 to 7; and

[0013] (b) a cocatalyst which activates the metallocene compound;wherein the ratio of meso to racemic forms of the metallocene in thecatalyst system is at least 1:3.

[0014] In this aspect of the invention no comonomer is added to theethyl and hydrogen during the polymerisation. This avoids the need toremove unwanted excess butene or other comonomer

[0015] In a further aspect, the preset invention provides use of ametallocene compound of general formula Ind₂R″MQ₂ as a component of acatalyst system for the production of a long chain branched polyethylenecopolymer in a solution or slurry process, wherein each Ind is the sameor different and is indenyl or substituted indenyl; R″ is a bridge whichcomprises a C₁ to C₄ alkylene radical, a dialkyl germanium or silicon orsiloxane, alkyl phosphine or amine, which bridge is substituted orunsubstituted, M is a Group IV metal or vanadium and each Q ishydrocarbyl having 1 to 20 carbon atoms or halogen; and the ratio ofmeso to racemic forms of the metallocene in the catalyst system is atleast 1:3.

[0016] In a further aspect, there is also provided a process for thepreparation of a polyethylene copolymer, which comprises polymerisingethylene, optionally with hydrogen, in a reaction medium which comprisesa solution or slurry of a catalyst system comprising

[0017] (a) a metallocene compound of general formula Ind₂R″MQ₂ asdefined in any one of claims 1 to 7; and

[0018] (b) a cocatalyst which activates the metallocene compound;wherein the ratio of meso to racemic forms of the metallocene in thecatalyst system is at least 1:3 so that the polyethylene formed therebyhas long chain branching.

[0019] In these further aspects the presence of comonomer in thereaction is optional. Advantageously, there is substantially nocomonomer present, thereby avoiding the need to remove unwanted excesscomonomer on completion of the reaction.

[0020] Each indenyl may bear one or more substituent groups, each ofwhich may be independently chosen from those of formula XR_(v) in whichX is chosen from group IVA, oxygen and nitrogen and each R is the sameor different and chosen from hydrogen or hydrocarbyl of from 1 to 20carbon atoms and v+1 is the valence of X. X is preferably C. If thecyclopentadienyl ring is substituted, its substituent groups must not beso bulky as to affect coordination of the olefin monomer to the metal M.Substituents on the cyclopentadienyl ring preferably have R as hydrogenor CH3. More preferably, at least one and most preferably bothcyclopentadienyl rings are unsubstituted. Each indenyl may be present inreduced form with up to 4 hydrogen substituents, such as in a 4, 5, 9, 7tetrahydroindenyl.

[0021] In a particularly preferred embodiment, both indenyls areunsubstituted.

[0022] R″ is preferably an ethylene bridge which is substituted orunsubstituted.

[0023] The metal M is preferably zirconium, hafnium or titanium, mostpreferably zirconium. Each Q is the same or different and may be ahydrocarbyl or hydrocarboxy radical having 1-20 carbon atoms or ahalogen. Suitable hydrocarbyls include aryl, alkyl, akenyl, alkylaryl oraryl alkyl. Each Q is preferably halogen. Ethylene bis(1-indenyl)zirconium dichloride is a particularly preferred bis indenyl compound ofthe present invention.

[0024] The metallocene catalyst component used in the present inventioncan be prepared by any known method. A preferred preparation method isdescribed in J. Org. Chem. 288, 63-67 (1985)

[0025] The cocatalyst which activates the metallocene catalyst componentcan be any cocatalyst known for this purpose such as analuminium-containing cocatalyst or a boron-containing cocatalyst. Thealuminium-containing cocatalyst may comprise an alumoxane, an alkylaluminium and/or a Lewis acid.

[0026] The alumoxanes used in the process of the present invention arewell known and preferably comprise oligomeric linear and/or cyclic alkylalumoxanes represented by the formula:

[0027] for oligomeric, linear alumoxanes and

[0028] for oligomeric, cyclic alumoxane,

[0029] wherein n is 1-40, preferably 10-20, m is 3-40, preferably 3-20and R is a C₁-C₈ alkyl group and preferably methyl.

[0030] Generally, in the preparation of alumoxanes from, for example,aluminium trimethyl and water, a mixture of linear and cyclic compoundsis obtained.

[0031] Suitable boron-containing cocatalysts may comprise atriphenylcarbenium boronate such astetrakis-pentafluorophenyl-borato-triphenylcarbenium as described inEP-A-0427696, or those of the general formula [L′-H]+[B Ar₁Ar₂X₃X₄]—asdescribed in EP-A-0277004 (page 6, line 30 to page 7, line 7).

[0032] Preferably, the same catalyst system is used in both steps (i)and (ii) of the process. The catalyst system is preferably employed in asolution polymerisation process, which is homogeneous, or a slurryprocess, which is heterogeneous. In a solution process, typical solventsinclude hydrocarbons with 4 to 7 carbon atoms such as heptane, tolueneor cyclohexane. In a slurry process it is advantageous to immobilise thecatalyst system on an inert support, particularly a porous solid supportsuch as talc, inorganic oxides and resinous support materials such aspolyolefin. Preferably, the support material is an inorganic oxide inits finally divided form.

[0033] Suitable inorganic oxide materials which are desirably employedin accordance with this intention include Group 2a, 3a, 4a or 4b metaloxides such as silica, alumina and mixtures thereof. Other inorganicoxides that may be employed either alone or in combination with thesilica, or alumina are magnesia, titania, zirconia, and the like. Othersuitable support materials, however, can be employed, for example,finely divided functionalized polyolefins such as finely dividedpolyethylene.

[0034] Preferably, the support is a silica having a surface areacomprised between 200 and 900 m2/g and a pore volume comprised between0.5 and 4 ml/g.

[0035] The amount of alumoxane and metallocenes usefully employed in thepreparation of the solid support catalyst can vary over a wide range.Preferably the aluminium to transition metal mole ratio is in the rangebetween 1:1 and 100:1., preferably in the range 5:1 and 50:1.

[0036] The order of addition of the metallocenes and alumoxane to thesupport material can vary. In accordance with a preferred embodiment ofthe present invention alumoxane dissolved in a suitable inerthydrocarbon solvent is added to the support material slurried in thesame or other suitable hydrocarbon liquid and thereafter a mixture ofthe metallocene catalyst component is added to the slurry.

[0037] Preferred solvents include mineral oils and the varioushydrocarbons which are liquid at reaction temperature and which do notreact with the individual ingredients. Illustrative examples of theuseful solvents include the alkanes such as pentane, iso-pentane,hexane, heptane, octane and nonane; cycloalkanes such as cyclopentaneand cyclohexane; and aromatics such as benzene, toluene, ethylbenzeneand diethylbenzene.

[0038] Preferably the support material is slurried in toluene and themetallocene and alumoxane are dissolved in toluene prior to addition tothe support material.

[0039] The polyethylene formed in accordance with the present inventionpreferably has long chain branching with a shear ratio of preferably atleast 20, more preferably at least 30, and still more preferably atleast 40 These properties confer upon the polyethylene goodprocessability characteristics and a smooth glossy surface.

[0040] Without wishing to be bound by any theory it is postulated thatcomonomer is not required in the polymerisation because butene is formedin situ at the active site of the metallocene catalyst, probably byethylene dimersation. Butene found in situ would react very quickly witha growing polymer chain because no diffusion barrier would be present.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The invention will now be described in further detail, by way ofexample only, with reference to the following Examples and theaccompanying drawings, in which:

[0042]FIG. 1 shows a 13C NMR spectrum of a polyethylene made inaccordance with the present invention; and

[0043]FIG. 2 shows a 13C NMR spectrum of a further polyethylene made inaccordance with the present invention.

BRIEF DESCRIPTION OF THE INVENTION EXAMPLE 1 Catalyst Preparation

[0044] (a) Synthesis of the Stereoisomers

[0045] High yield rapid synthesis of therac/meso(bisindenyl)ethanezirconium dichloride: The freshly prepareddiaromatized bisindenylethane ligand is suspended in pentane and reactedwith an equimolar suspension of ZrCl₄ in pentane. The slurry is stirredfor three Hours and filtered. Yellow solid is extracted with methylenechloride to separate the LiCl. According to NMR of the crude product amore or less quantitative yield for the rac/meso mixture is obtainedaccording to this method.

[0046] (b) Isolation of the Pure Stereoisomers

[0047] Solubility test showed that the meso isomer has about three timeshigher solubility in toluene. In this way the meso can be concentratedin toluene and completely separated from the racemic byproduct.

[0048] The support used in a silica having a total pore volume of 4.217ml/g and a surface area of 322 m^(2/)g. This silica is further preparedby drying in high vacuum on a schlenk line for three hours to remove thephysically absorbed water. 5 g of this silica are suspended in 50 ml oftoluene and placed in a round bottom flask equipped with magneticstirrer, nitrogen inlet and dropping funnel.

[0049] An amount of 0.31 g of the metallocene is reacted with 25 ml ofmethylalumoxane (MAO 30 wt % in toluene) at a temperature of 25° C.during 10 minutes to give a solution mixture of the correspondingmetallocenium cation and the anionic methylalumoxane oligomer.

[0050] Then the resulting solution comprising the metallocenium cationand the anionic methylalumoxane oligomer is added to the support under anitrogen atmosphere via the dropping funnel which is replacedimmediately after with a reflux condenser. The mixture is heated to 110°C. for 90 minutes. Then the reaction mixture is cooled down to roomtemperature, filtered under nitrogen and washed with toluene.

[0051] The catalyst obtained is then washed with pentane and dried undera mild vacuum.

EXAMPLE 2

[0052] Polymerisation Procedure and Results

[0053] Ethylene was polymerised under the conditions described in Table1 in a 4 l batch reactor at a temperature of 80° C. for a residence timeof 60 mins. Supported catalyst was precontacted withtriisobutylaluminium (TBAC) and introduced into the reactor in which 2 lof isobutene were used as diluent. The metallocene was present at 100 mgand the cocatalyst at 390 ppm. TABLE 1 Part 1 Hydrogen Comonomer YieldHourly Prod M12 HLMI Density Bulk Density Run (wt %-NL) (wt %) (g)(g/g.hr) (g/10′) (g/10′) SR (g/cc) (g/cc) A 0 0.00 183 1830 0.14 8.47 600.9438 0.28 B 0 1.22 250 2500 0.65 27.06 42 0.9385 0.37 C 0 2.44 3463460 1.23 40.31 33 0.9380 0.27 D 0 3.66 390 3900 2.47 74.42 30 0.95500.29 E 0 4.88 270 2700 4.98 152.40 31 0.9521 0.30 F 0.25 0.00 166 16601.94 65.94 34 0.9530 0.36 G 0.25 1.22 345 3450 0.78 28.57 37 0.9623 0.35H 0.25 2.44 255 2550 4.75 157.60 33 0.9429 0.31 I 0 0.00 338 3380 0.063.75 60 0.9574 0.24 J 0 2.44 695 6950 0.14 8.63 62 0.9366 0.35 K 0.252.44 676 6760 0.54 21.76 40 0.9421 0.39 L 0.25 3.66 720 7200 0.58 23.3740 0.9407 0.34 M 0.25 4.88 922 9220 0.72 25.38 35 0.9394 0.32 Part 2Hydrogen Comonomer Mn Mw Mz Mp Run (wt %-NL) (wt %) (kDa) (kDa) (kDa)(kDa) D D′ A 0 0.00 28.376 134.8 451.0 94 4.7 3.4 B 0 1.22 26.388 101.6334.6 53 3.9 3.3 C 0 2.44 23.139 94.6 354.7 45 4.1 3.8 D 0 3.66 22.84875.0 215.0 42 3.3 2.9 E 0 4.88 19.658 64.6 202.0 32 3.3 3.1 F 0.25 0.0015.320 88.8 421.4 43 5.8 4.7 G 0.25 1.22 25.920 105.7 366.3 56 4.1 3.5 H0.25 2.44 17.528 73.6 262.8 37 4.2 3.6 I 0 0.00 37.464 155.2 528.2 654.1 3.4 J 0 2.44 34.036 122.0 375.5 60 3.6 3.1 K 0.25 2.44 25.657 115.1423.9 56 4.5 3.7 L 0.25 3.66 25.164 110.3 402.4 52 4.4 3.6 M 0.25 4.8827.277 99.5 335.1 49 3.7 3.4

[0054] Table 1 represents the polymerisation conditions, results andpolymer analysis for the meso stereoisomer. The polymerization activityincreases with increasing comonomer content in the feed regardless ifhydrogen is present or not. A maximum activity of 4000 g PE/g cat for 6%ethylene and 1000 g PE/g cat for 10% ethylene concentration has beenreached with different hexene concentration at this stage. The densitybehaviour is also interesting with respect to the hexene concentration;it does not decrease gradually with increasing hexene concentration.This behaviour is related to the in situ butene formation (cf. 13C NMR).For a monomodal polymer formed with a single site catalyst the SRs ofthe polymers are very large (35-60). The most important practicalconsequence of large SR, related to long chain branching (cf 13C NMR),is the fact that the specimens that have been obtained from the meltindexer show no signs of melt fracture (good processibility) and thecorresponding plaques are of very smooth and glossy surfaces.

[0055] 13C NMR Analysis of PE Homo- and Copolymers

[0056] Table 2 sets out the results of 13C NMR analysis of thepolyethylenes produced under the conditions of some of the runs detailedin Table 1. The averages of three NMR analyses are shown. Representativespectra from runs A and C are shown in FIGS. 1 and 2 respectively. Thespectra indicate a very good comonomer incorporation capability and theformation of long chain branching. In addition to the hexene (Butanebranching) substantial amounts of butene (ethyl branching) are observedin the backbone of the polymers. Most important is the signal pattern ofthe spectrum in FIG. 1 of the polymer produced in the absence of anytype of external comonomer. It shows up to 1 wt % Butene and confirmsthe in situ formation of butene via dimerization of ethylene. Since noother signals related to other comonomers is observed it can beconcluded that the dimerization mechanism is very specific. Theformation of long chain branching and comomoner is part of the uniqueproperties of this catalytic system. Hydrogen Comonomer (wt %-NL) (wt %)% C4m % C4w % C6m % C6w A 0 0 0.44 0.88 0 0 B 0 1.22 0.38 0.75 0.44 1.31C 0 2.44 0.27 0.53 0.75 2.21 D 0 3.66 0.26 0.51 1.14 3.32 E 0 4.88 0.300.58 1.72 4.97 G 0.25 1.22 0.28 0.57 0.17 0.52 I 0 0 0.37 0.74 0 0 J 02.44 0.33 0.65 0.50 1.48 L 0.25 3.66 0.24 0.48 0.49 1.45

1. A catalyst comprising a metallocene compound of general formulaInd₂R″MQ₂, wherein each Ind is the same or different and is indenyl orsubstituted indenyl; R″0 is a bridge which comprises a C₁ to C₄ alkyleneradical, a dialkyl germanium or silicon or siloxane, alkyl phosphine oramine, which bridge is substituted or unsubstituted, M is a Group IVmetal or vanadium and each Q is hydrocarbyl having 1 to 20 carbon atomsor halogen; and the ratio of meso to racemic forms of the metallocene inthe catalyst system is at least 1:3.
 2. A catalyst according to claim 1,wherein R″ is an ethylene bridge, which is substituted or unsubstituted.3. A catalyst according to claim 1, wherein the cyclopentadienyl ring ofat least one of the indenyls is unsubstituted.
 4. A catalyst accordingto claim 3, wherein both indenyls is unsubstituted.
 5. A catalystaccording to claim 1, wherein M is Zr.
 6. A catalyst according to claim1, wherein the Q is halogen.
 7. A catalyst according to claim 1, whereinthe bis indenyl compound is ethylbenzene 1-indenyl-zirconium dichloride.8. A catalyst accordingly to claim 1, wherein the catalyst furthercomprises a cocatalyst capable of activating, the metallocene compound.9. The catalyst according to claim 8, wherein the cocatalyst, whichactivates the metallocene compound, comprises an aluminum-containingcocatalyst or a boron-containing cocatalyst.
 10. A catalyst according toclaim 8, wherein the cocatalyst comprises an aluminum-containingcocatalyst comprising an alumoxane, an alkyl aluminum and/or a Lewisacid.
 11. A catalyst according to claim 1, wherein the catalyst furthercomprises an inert support.
 12. A process for the preparation of apolyethylene copolymer, which comprises polymerization ethylene,optionally with hydrogen, in a substantially comonomer-free reactionmedium which comprises a catalyst comprising (a) a metallocene compoundof general formula Ind₂R″MQ₂, wherein each Ind is the same or differentand is indenyl or substituted indenyl; R″ is a bridge which comprises aC₁ to C₄ alkylene radical, a dialkyl germanium or silicon or siloxane,alkyl phosphine or amine, which bridge is substituted or unsubstituted,M is a Group IV metal or vanadium and each Q is hydrocarbyl having 1 to20 carbon atoms or halogen; and the ratio of meso to racemic forms ofthe metallocene in the catalyst system is at least 1:3. (b) a cocatalystwhich activates the metallocene compound; wherein the ratio of meso toracemic forms of the metallocene in the catalyst system is at least 1:3.13. A process according to claim 12, wherein the polyethylene formedthereby has short chain branching arising from C₄ incorporation in thebackbone of the polyethylene.
 14. A process according to claim 12,wherein the polyethylene formed thereby has long chain branching.
 15. Aprocess according to claim 14, wherein the polyethylene formed therebyhas a shear ratio of at least
 20. 16. A process according to claim 12,wherein the catalyst further comprises an inert support.
 17. A longchain branched polyethylene copolymer formed by a process comprisingcopolymerization ethylene, optionally with hydrogen, in a reactionmedium, which comprises a solution or slurry of a catalyst comprising(a) a metallocene compound of general formula Ind₂R″MQ₂; and (b) acocatalyst, which activates the metallocene compound; wherein the ratioof meso to racemic forms of the metallocene in the catalyst system is atleast 1:3 so that the polyethylene formed thereby, has long chainbranching.
 18. A catalyst according to claim 17, wherein R″ is anethylene bridge, which is substituted or unsubstituted.
 19. 3. Acatalyst according to claim 17, wherein the cyclopentadienyl ring of atleast one of the indenyls is unsubstituted.
 20. A catalyst according toclaim 17, wherein both indenyls are unsubstituted.
 21. A catalystaccording to claim 17, wherein M is Zr.
 22. A catalyst according toclaim 17, wherein the Q is halogen.
 23. A catalyst according to claim17, wherein the bis indenyl compound is ethylbenzene 1-indenyl zirconiumdichloride.
 24. 8. A catalyst accordingly to claim 17, wherein thecatalyst further comprises a cocatalyst capable of activating themetallocene compound.
 25. The catalyst according to claim 17, whereinthe cocatalyst, which activates the metallocene compound, comprises analuminum-containing cocatalyst or a boron-containing cocatalyst.
 26. Acatalyst according to claim 17, wherein the cocatalyst comprises analuminum-containing cocatalyst comprising an alumoxane, an alkylaluminum and/or a Lewis acid.
 27. A catalyst according to claim 17,wherein the catalyst further comprises an inert support.